With the proliferation of email communications has come a proliferation in the amount of unsolicited and unwanted email messages. Unsolicited bulk email (“UBE”), which also is referred to as “SPAM” makes up a huge amount of network traffic worldwide. According to some estimates, close to 100 billion unsolicited and/or unwanted SPAM messages were sent on average per day in 2013. Although some studies indicate that the incidence of SPAM messages has since declined, SPAM messages continue to account for a large amount of network traffic. Also, SPAM messages often are the source of malware such as adware, viruses, and the like, which can adversely impact computer users and/or consume additional networking and computing resources.
Various approaches have been introduced over the years to attempt to reduce the amount of SPAM messages sent and/or received by users. The use of keys has been used to ensure that a sender or recipient have a trust relationship, though this requires a sender and recipient to exchange keys with one another. Some other approaches to avoiding SPAM have relied on various algorithms for identifying probable SPAM messages, though these algorithms often are not foolproof and can result in blocked legitimate messages. Some other approaches limit the amount of messages that can be sent or received by users, though these approaches also can impact legitimate email communications.